Optical navigation apparatus are used in portable electronic appliances as a user input device for graphic user interface (GUI) control. Optical navigation apparatus operates by registering relative movement between the optical navigation apparatus and a target sensing surface in close proximity to the sensing area of the apparatus and convert the movement information into electronic format accessible by external system. An optical navigation apparatus uses a light source, such as a light emitting diode (LED) or laser to illuminate user's finger and a sensor to capture reflected light off the target surface. The control logic within the optical navigation apparatus compares consecutive changes in reflected light pattern and estimates the relative movements between the optical navigation apparatus and the target surface based on the comparison. Typical optical navigation apparatus output two-dimensional movement information that represents the two-dimensional movement of the finger relative to the sensor array. The two-dimensional movement information is then used to move a cursor on a display of a corresponding computing device.
Optical navigation apparatus can be used to move a cursor on a display and the graphical user interface of many computing devices, such as personal computer, telephone, smart phones, and personal digital assistants (PDA). For example, the optical navigation apparatus is commonly used as the main navigation button on a mobile phone. As the user finger moves on the apparatus surface, the motion is tracked and the movement is reflected in the cursor movement on the display screen of the phone.
A traditional optical navigation apparatus includes an outer housing, an infrared source and a sensor array positioned in close proximity. The sensor array and the infrared source are mounted on a substrate, e.g. a printed circuit board. The infrared light source is formed within the outer housing to illuminate the target surface on which finger motion are performed. Commonly, the optical navigation apparatus may further includes a light guide for guiding infrared light to illuminate the target surface. Since the sensors in the optical navigation apparatus are often sensitive to both visible light and infrared, the outer housing of the apparatus is made of infrared-transparent that blocks visible light transmission to prevent light interference from the surroundings.
On the other hand, it is common for portable electronic appliance to have user input keys that are illuminated on the front-facing surface to facilitate operation in low-light environment. For better visual effect, the illumination pattern need to have high uniformity and clearly defined character shape. With the previous apparatus design, it is not possible to achieve this illumination effect as visible light is blocked from transmission through the outer housing walls. Hence, it is desired to provide an improved optical navigation apparatus to overcome the above-mentioned drawbacks.